Method for manufacture of di-calcium phosphate



' Patented Apr. 8, 1930 PATIENT OFFICE ROBERT D. PIKE, OF OAKLAND, OBIIIEORNIA METHOD FOR MANUFACTURE OF DI-CALCIUM PHOSPHATE N Drawing.

drochloric acid gas, which is mixed with gases of combustion.

of gases of combustion and hydrochloric acid gas into direct contact with ground-phosphate rock which is suspended in water. This ma be done in any suitable form of Well bubble tower, but'I find it preferable to use apparatus similar to that described in my above mentioned co-pending application Serial Number 228,177. In utilizing this apparatus the hydrochloric acid laden gases of combustion at a temperature of 300500 Centigrade are caused to flow by the rotating graphite blades which are utilized for stirring the water suspension of pulverized phosphate rock. Heat is transferred to these blades and the film of Water which covers them absorbs HCl. The net result is a rapid 'anclietficient decomposition of the phosphate roc As an example of this stepof my process, consider the use of a western phosphate rock in which the ratio of .CaO to P 0 is 1.4.93/1. It is preferable to grind this rock so that 80% is less than 100 mesh and then to roast in a mechanical externally fired roaster at a temperature of 600-700 C. Pulverized roasted rockis mixed with water and passed through the apparatus for contacting with the HCl gas. It is preferable to employ from three to four parts by weight of water to one part by weight of the pulverized rock. The apparatus should be so proportioned that the suspension of phosphate rock and water is kept in contact with the HCl gas for not less than six hours. As a result of this re- In my present process I bring this mixture Application filed November 14, 1927. Serial No. 233,322.

action over 95% of the P20 goes into solution and. the liquid is separated from the silicous residue by any suitable Well known means. The clarified solution contains from five to seven per cent of P 0 depending upon-the raito of water to roasted rock and upon the P 0 content of the later. 'The ratio of P 0 as mono calcium phosphate to the P 0 as phosphoric acid is about 2.64 to 1. There is from 1 to 1.5% of free H01 in the solution.

. Fox and Whittaker,Jour. Ind. Eng. Chem.

19, 349 (1927) state that if calcium carbonate is used to effect precipitationof such a solution, a considerable amount of non-available tricalcium phosphate is formed. I have found that if I neutralize the free hydrochloric acid and the first hydrogen ion of the free phosphoric acid present with calcium car 20 known apparatus such. for example, as a tray bonatc, andthen preciptate the remaining P 0 with milk of lime, I get a satisfactorily available precipitate which after filtering,

washing, and. drying, contains about 40% P 0 soluble in standard ammonium citrate solution,

A principal advantage of my method is that a considerable part of the calcium required forprecipitation is added as cheap calcium carbonate; a further advantage is that less heat is generated by the reaction than is the casewhen all of the lime is added as milk oflime, and the cooler condition of the solution tends to promote formation of available, rather than non-available phosphates.

It will be understood that many of the details concerning proportions, temperatures, etc., are subject to considerable variation without departing from the spirit of my invention, as disclosed in the appended claims.

Having thus described my invention, What I claim and desire to secure by Letters Patent is I 1. The process for utilizing gaseous hydrochloric acid and producing available dicalcium phosphate, which consists in bringing gaseous hydrochloric acid into contact with a water suspension of pulverized phosphate rock, thereby decomposing the phosphate rock and taking into solution phosphoric acid and mono calcium phosphate,-

adding calcium carbonate to this solution to neutraliz the first hydrogen ion of its free phosphoric acid'and its hydrochloric acid, then precipitating di-calcium phosphate with calcium hydroxid, and separating the precipitate from the solution.

2. The step in the proccss for producing dicalcium phosphate from solutions containing mono calcium phosphate, phosphoric acid and hydrochloric acid, which consists in adding calcium carbonateto neutralize the hydrochloric acid and the first hydrogen ion of the free phosphoric acid,then precipitating the di-cal'cium phosphate by adding calcium hydroxid, and separating the precipitate from the solution.

' a ROBERTD. PIKE. 

